2012 Annual Report
1a.Objectives (from AD-416):
Available nutrient levels within many soils impose limits on overall plant productivity and yield. For food security, future agricultural practices will need to incorporate important traits for nutrient use efficiency to generate elite high-yielding crops.
Although it has long been known that nutrient acquisition by the roots is controlled by root-to-shoot and shoot-to-root signaling systems, currently little is known regarding the molecular components that function in these pathways. Recently, analysis of phloem sap collected from plants subjected to nutrient deprivation, identified a number of small RNA species that may mediate in the epigenetic regulation of ion acquisition by the roots.
1b.Approach (from AD-416):
To further explore this possibility, we plan to utilize the cucumber genome, in combination with our ability to collect analytical quantities of phloem sap from this species, to identify and characterize potential siRNA, miRNA and mRNA molecules involved in regulating nutrient acquisition by the root system. Next, we will identify the phloem proteins that deliver such candidate RNA species to the root, as well as the cells targeted for regulation. Finally, we plan to explore the gene regulatory network(s) that operates within these target tissues to allow plants to adapt to the ever changing nutrient availability within the soil. These studies will provide insights into the mechanisms that evolved to allow plants to coordinate nutrient acquisition by the root with developmental and physiological processes occurring within the above-ground regions of the plant. As an important outcome, this knowledge would contribute towards the engineering of crops having enhanced nutrient use efficiency.
In the first year of this grant, we developed the methods to grow cucumber plants in sand culture where the plants are supplied with sufficient or low levels of phosphorous (P). We also developed the methods to collect the phloem sap moving from the shoot to the root and will be analyzing that phloem sap using next generation sequencing methods for RNA molecules. These would become candidate P signaling molecules transported from the shoot to the roots indicating the plant is experiencing P deficiency. This in turn triggers a cascade of events (changes in root architecture, increased expression of P uptake genes, etc) that the plant uses to increase P acquisition.